Question

我是论坛的新手，我遇到了问题。

在Django中尝试通过OnetoOneField将其引用到用户对象来创建UserProfile类。当我尝试迁移时，我得到：

“您试图在没有默认值的情况下向作者添加不可为空的字段'id';我们不能这样做（数据库需要填充现有行的内容）。请选择一个修复： 1）现在提供一次性默认值（将在所有现有行上设置） 2）退出，让我在models.py“

中添加默认值

据我所知，User模型中有一些字段（例如“id”）不允许为null。

当我尝试设置默认值时，它会生成迁移，但迁移失败并出现语法错误。

我的问题是如何在不编写自定义用户类的情况下允许Null或设置默认设置，甚至是可能的？

我真的很感激任何帮助。

这是我的代码：

from django.db import models
from django.contrib.auth.models import User as User_django

class User(User_django):
    pass

class Author(models.Model):
    user = models.OneToOneField(User, null=True)

class BaseElement(models.Model):

    author=models.ForeignKey(Author, null=True)
    upvotes = models.PositiveIntegerField(default=0)
    downvotes = models.PositiveIntegerField(default=0)
    created = models.DateTimeField(auto_now_add=True, null=True)

    def vote_up(self):
        self.upvotes.value = self.upvotes.value + 1

    def vote_down(self):
        self.downvotes.value = self.downvotes.value + 1

    class Meta:
        abstract = True


class Post(BaseElement):
    content = models.TextField(max_length=240)
    tags = models.CharField(max_length=40, blank=True)
    said_by = models.CharField(max_length=40)
    said_at = models.CharField(max_length=40, blank=True)

    def get_comments(self):
        return self.comment_set.all()

    def get_comments_anzahl(self):
        return self.comment_set.all().count()


class Comment(BaseElement):
    content = models.TextField(max_length=140)
    commented_post = models.ForeignKey(Post, related_query_name="comment", null=True)

编辑：

如果我尝试设置默认值并尝试迁移，则会发生这种情况：

You are trying to add a non-nullable field 'id' to author without a  
default; we can't do that (the database needs something to populate 
existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can  
do e.g. timezone.now()
>>> 1
 Migrations for 'post':
 0003_auto_20160505_1237.py:
  - Change Meta options on author
  - Change managers on author
  - Remove field user_ptr from author
  - Add field id to author
  - Add field user to author

 Operations to perform:
 Apply all migrations: contenttypes, admin, sessions, post, auth
 Running migrations:
   Rendering model states... DONE
   Applying post.0003_auto_20160505_1237...Traceback (most recent call last):
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
   return self.cursor.execute(sql, params)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/sqlite3/base.py", line 323, in execute
   return Database.Cursor.execute(self, query, params)
   sqlite3.OperationalError: near ")": syntax error

  The above exception was the direct cause of the following exception:

 Traceback (most recent call last):
    File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django  /core/management/__init__.py", line 353, in execute_from_command_line
   utility.execute()
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/core/management/__init__.py", line 345, in execute
   self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/core/management/base.py", line 348, in run_from_argv
   self.execute(*args, **cmd_options)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/core/management/base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/core/management/commands/migrate.py", line 200, in handle
   executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/migrations/executor.py", line 92, in migrate
    self._migrate_all_forwards(plan, full_plan, fake=fake,  fake_initial=fake_initial)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/migrations/executor.py", line 198, in apply_migration
   state = migration.apply(state, schema_editor)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/migrations/migration.py", line 123, in apply
   operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/migrations/operations/fields.py", line 121, in database_forwards
   schema_editor.remove_field(from_model, from_model._meta.get_field(self.name))
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/sqlite3/schema.py", line 247, in remove_field
    self._remake_table(model, delete_fields=[field])
    File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/sqlite3/schema.py", line 197, in _remake_table
    self.quote_name(model._meta.db_table),
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/base/schema.py", line 110, in execute
    cursor.execute(sql, params)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/utils.py", line 79, in execute
     return super(CursorDebugWrapper, self).execute(sql, params)
    File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
    File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/utils.py", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/utils/six.py", line 685, in reraise
    raise value.with_traceback(tb)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
   return self.cursor.execute(sql, params)
   File "/home/jaidmin/.conda/envs/cyf/lib/python3.5/site-packages/django/db/backends/sqlite3/base.py", line 323, in execute
    return Database.Cursor.execute(self, query, params)
   django.db.utils.OperationalError: near ")": syntax error

编辑：似乎我通过创建一个新项目并逐步复制模型和迁移来解决它。仍然想知道那里发生了什么，因为我刷新了数据库并多次删除了迁移文件，但它仍然在抛出错误。

感谢您的帮助！

Answer 1

看看这个：

https://docs.djangoproject.com/es/1.9/topics/db/examples/one_to_one/

您的代码与用户是一对一的。设置它时，它意味着CASCADE删除，因此永远不能为空。

如果您更改为一对多，并且只确保您只为外键插入一个对象，它将起作用。否则，请更改级联规则。

但是，我会说，这不是一个好主意，因为如果你把它设为null，那么它将它与其他记录区分开来。考虑第二个PK领域。

祝你好运。

Answer 2

只需导入django的内置User模型，如下所示：

from django.contrib.auth.models import User

并删除此行：

class User(User_django):
    pass

来自您的代码，因为它完全没必要。

更新：此外，您的问题似乎与User模型无关。我想某种程度上你为你的Author模型添加了一个id字段并将其删除（可能是在迁移失败后）。如果是这种情况，那么您可以修改0003_auto_20160505_1237.py。要做到这一点，打开它并删除看起来像这样的行：

migrations.AddField(
    model_name='author',
    name='id',
    field=models.someFieldType(options)),
),

再试一次。

Django模型与用户模型的关系

2 个答案: